[24a-E303-1~11] 3.12 Nanoscale optical science and near-field optics

▲ [24a-E303-6] Surface lattice resonances coupled to mid-infrared plasmonics based on ZnO: Ga

〇(D)Shuting Ma¹, Ikuya Ando¹, Yuta Shimoda¹, JQ. Yang¹, Hidehiko Yoshida², Hitoshi Tabata¹, Hiroaki Matsui¹ (1.The Univ. of Tokyo, 2.Utsunomiya Univ.)

Keywords:surface lattice resonances, biosensing platform, ZnO: Ga microdot array

Biosensing devices with molecular recognition are important methods to monitor dynamic processes of biological reactions. Surface plasmon resonances (SPRs) can enhance molecular vibrations in the mid-infrared range, which can clear presence of biomolecules on sensing surfaces. Our research groups have developed infrared plasmonics based on oxide semiconductors. In this work, we focus on ZnO: Ga microdot arrays as a source of mid-infrared SPRs for biosensing platforms. In particular, we employ surface lattice resonances (SLRs) in an effort to enhance quality factor of SPRs. When plasmonic nanoparticles are arranged in a highly ordered array, the diffracted wave propagating across the array plane would couple with the plasmon resonance from a single particle, leading to narrowing of plasmonic resonance due to optical coupling of SPRs to SLRs (SPR-SLR coupling). In this research, we fabricated ZnO: Ga microdot arrays with a dot size (D) of 4 mm on CaF₂ substrates by photo-lithography and pulsed laser ablation. To elucidate the excitation mechanism of SPR-SLR coupling, we fabricated ZnO: Ga microdot arrays with different lattice periods (L = 2 - 10 mm). The increase in lattice period resulted in a red-shift of resonant peak, indicating that the resonant peaks of the microdot arrays were attributed to far-field coupling between microdots via their scattered radiation fields. Furthermore, we investigated change in resonant peak when the microdot arrays were placed on various substrates with different refractive indices. The resonant peaks gradually shifted to lower wavenumbers with increasing the refractive index, which clarified that the resonant peaks were derived from electric-fields at interfaces between microdots and substrates. Secondly, we examined the resonant behaviors of the microdot arrays excited along the in-plane (s-pol.) and out-of-plane directions (p-pol.) at different incident angles using infrared ellipsometry.